This invention is directed generally to fluid warming apparatus and, more particularly, to an apparatus for warming cold parental fluids such as whole blood for intervenous injection or transfusion procedures.
Whole blood is commonly stored in blood banks at a temperature of 4.degree. C. until infused into a patient, at which time it is necessary that the blood be warmed to or slightly below the 37.degree. C. temperature of the human body if hypothermia and the attendant risk of ventricular fibrillation and cardiac asystole are to be avoided. For applications where substantial and unpredictable quantities of blood are required, as where a patient hemorrages during surgery, it is preferable that blood in storage be transferred substantially directly into the patient, since this avoids warming blood which is not subsequently used.
The present invention provides an effective and efficient system for dry warming blood or other parental fluids to body temperature during the process of infusing such fluids into the patient. It is a feature of the invention that the temperature of the infused blood is maintained substantially constant at 37.degree. C. substantially independent of flow rates, which may vary from 0 to 150 ml per minute depending on the needs of the patient. A further feature is that the operation of the apparatus, as well as the temperature of the blood leaving the apparatus, is continuously monitored, and in the event of a malfunction operation is terminated and an alarm is sounded. Novel self-test provisions within the apparatus allow the operator to verify the operation of these monitoring circuits prior to placing the blood warming apparatus in service.
Sterility of the blood is maintained and contamination of the apparatus is avoided by use of a disposable flow system having a blood warming bag which fits within the apparatus in thermal communication with electric heating elements. An additional feature of the invention provides an alarm in the event of inadvertent removal of the blood processing bag from the apparatus, and AC-coupled sensing circuitry which measures the temperature of the blood at the inlet and outlet portions of the blood processing bag automatically controls the operation of the heating elements to more accurately maintain the output temperature of the blood.
Accordingly, it is a general object of the present invention to provide a new and improved apparatus for warming blood and other parental fluids prior to infusion into the human body.
It is another object of the present invention to provide new and improved apparatus for maintaining blood and other parental fluids at a substantially constant temperature over a wide range of flow rates.
It is another object of the present invention to provide new and improved blood warming apparatus which provides improved protection against malfunction.
It is another object of the present invention to provide a new and improved blood warming apparatus which is convenient to operate and requires a minimal amount of operator supervision.
It is another object of the present invention to provide a new and improved blood warming apparatus which requires a minimal set-up time and may be conveniently set-up and operated in a variety of different environments.